Answers
1

Smerdyokov is the direct murderer, although Dmitri is charged with the murder (so technically he's the guilty one). Grushenka refers to herself several times throughout the novel, saying she's responsible for the murder (indirectly) because of her relationship with Fyodor and Dmitri (inciting Dmitri to kill his father)

Source(s)

I just read the book, and that's how I understood the answer to your question